Wheelchairs are typically intended to provide independent mobility for persons without the use of their legs, and provide means of utilizing arm movement to cause rotation of one or more wheels of the wheelchair. In the commonest and simplest form, round pushrims of slightly smaller diameter than the propelling wheels are fixed to the said propelling wheels, such that the user may conveniently grasp the pushrims to exert a rotational torque to the driving wheels through the pushrims. Although such means of propelling is
simple, light in weight, and inexpensive, problems with pushrims include placing the users hand near the tires of the driving wheels which may be dirty, requiring considerable grip strength to grasp the pushrim, and repetitive motion injuries from the non-optimal bio-mechanics of grasping and pushing the pushrims. Efforts to provide solutions to these problems have often included lever drive mechanisms that allow the user to propel with reciprocating rowing type of motion. The levers can be located such that the pushing and pulling on the grip portion of the input lever provides improved biomechanics and keeps the users hand away from the driving wheels. Torque transmission from the input lever to the driving wheels typically involves some type of clutch action such that the wheelchair can be propelled in both forward and reverse directions. In this type of drive mechanism a means must be provided to allow the user to select either forward or reverse, and also to disengage the drive mechanism so that the wheelchair can be pushed by a caregiver.